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Astronomy
A S T R O N O M Y
Glossary of Astronomical Terms
Astronomical Coordinate Systems
Altitude and Azimuth - relative to horizon of the observer.
Right ascension and declination) - tied to the celestial sphere and rotate with it.
Astronomical Magnitude [m]
Indicates the visual brightness of an object. Positive = dim, Negative = bright
6m is the bightest visible to the eye. The brightest star (Sirius) reaches 0m
Venus, the brightest planet, reaches -4m, and the moon at first quarter is -8m,
Azimuth
Azimuth defines a point on the horizon in degrees counting from geographic North clockwise to the East.
(i.e. angular distance around the horizon, where north is 0 degrees, east is 90 degrees.)
Altitude (degrees)
The altitude of a celestial object is its angular distance above the horizon.
The altitude of an object on the horizon is 0°, and at the zenith is 90°.
Right Ascension
Right Ascension (R.A.) is similar to longitude on the Earth, and is measured in hours of time
along the celestial equator (divided into 24 equal portions). 0 hours is a point on the celestial equator called the vernal or March equinox.
Declination
Declination is measured in degrees, and refers to how far above the imaginary "celestial equator" an object is.
It is measured as 0 degrees at the equator, +90 degrees at the North Pole, and -90 degrees at the South Pole.
(Polaris, the North Star, is close to declination +90)
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